Failure to find an absolute retinal limit of a putative short-range process in apparent motion.

Previous studies of apparent movement have concluded that the short-range process does not operate when stimulus displacements exceed 15-20' arc. In the present experiments, we studied a bistable apparent-movement display, one of whose perceptual organizations is mediated by short-range process. In both experiments it was found that the perceptual organization mediated by the short-range process could be made dominant at stimulus displacements well in excess of the proposed spatial limit, provided the stimulus elements were made larger. It is concluded that the spatial limit of the short-range process is a relative, not absolute, one. Current knowledge regarding the short-range process is reviewed, and an hypothesis regarding the functional utility of the short-range process in compensating for the effects of small eye tremors is advanced.